The present invention relates generally to systems and methods for ion implantation, and more particularly, to such systems and methods that allow facile and accurate measurement of energy of an ion beam utilized for implanting ions in a substrate.
Ion implantation is used routinely in many material-processing applications. For example, in SIMOX (separation-by-implantation-of-oxygen) applications, oxygen ions can be implanted into a semiconductor substrate, e.g., a silicon wafer, to generate a buried insulating layer, e.g., SiO2, through subsequent annealing steps. In many such applications, the energy of the ions impacting a substrate needs to be in a predefined range to ensure obtaining a desired effect. For example, in SIMOX processing, the penetration depth of ions in a wafer can be varied by choosing different energies for an ion beam impacting the wafer.
Controlling the energy of the ions requires the ability to measure the ion energy. In many ion implantation systems, ions transit through a number of stages that can provide charge selection, acceleration and beam forming. The ions can be subjected to voltage differentials at one or more of these stages, each of which can change the ion energy. Hence, determining the ion energy can be a time-consuming process that may require multiple measurements, additions and/or subtractions, each having an associated error.
Thus, there is a need for enhanced methods and systems for accurately measuring the energy of ions in an ion implantation system.
There is also a need for such methods and systems that allow readily measuring the ion energy in an ion implantation system without the need for performing multiple measurements.
The present invention provides an ion implantation system that can include an ion source maintained at a high electric potential for generating ions of a selected species. The implantation system can further include a plurality of extraction electrodes that accelerate the ions from the source to an end station that is maintained at a nominal ground electric potential. A wafer holder disposed at the end station can hold a wafer in the path of the accelerated ions. The implantation system is further characterized by a high voltage probe that is disposed between a high voltage terminus of the ion source and ground. The high voltage probe advantageously allows direct measurement of the energy of an ion beam utilized for implantation.
In another aspect, the high voltage probe can measure voltages corresponding to maximum beam energy that an implanter in which the probe is incorporated can provide, for example, 300 volts. Further, the high voltage probe can include a voltage divider that is configured to generate a calibrated ratio of a voltage applied across the probe. The voltage ratio is preferably in a range that can be safely and readily read out, for example, by a voltmeter. For example, the calibrated ratio can be 30,000:1.
In a related aspect, the high voltage probe can contain a fluid, for example, SF6 gas, that exhibits a high dielectric breakdown strength so that the probe can be manufactured with physical dimensions that are not exorbitantly large.
Further understanding of the invention can be obtained by reference to the following description in conjunction with the drawing which is described briefly below.